1. Field of the Invention
This invention relates to a fluid sampling apparatus, and more particularly, to an apparatus for obtaining a liquid sample such as a specimen of blood or the like and for delivering the sample to means for analyzing it.
2. Description of Related Art
Preparatory to analysis, a sample of whole blood is drawn from a patient and typically stored under negative pressure (i.e., a pressure less than atmospheric) in a glass tube with a rubber stopper, such as the type sold under the trade designation `Vacutainer` by Becton-Dickenson and Company of East Rutherford, N.J. The blood in this tube is gently and carefully mixed to obtain an even distribution of blood cells either by use of a separate mixing device followed by removal of the rubber stopper and aspiration of an aliquot of blood into a blood analyzer, or by automated mixing and subsequent sampling from a closed container using devices such as described in my U.S. Pat. No. 4,120,662 and my U.S. Pat. No. 4,311,484 (the '484 patent).
The specimen sampling apparatus described in the '484 patent mixes the contents of a series of specimen tubes and delivers them sequentially to a sampling station where a needle, which is connected via a conduit to the intake of a suitable analyzer such as a "Coulter Counter" Model S By Coulter Electronics, Inc. of Hialeah, Fla., penetrates the rubber stopper for aspiration of a specimen sample from the tube into the needle and thence through a conduit with subsequent delivery of blood to the analyzer blood metering system.
Typically, in using the Coulter Counter Model S, 1 ml of blood would be drawn from the storage tube and transported through the lines of the apparatus with about 0.044 ml of blood actually being subjected to dilution for analysis. In many of these apparatuses, various blood samples could and did abut one another in the lines or conduits of the sample probe and blood metering valve of the apparatus while the blood was being transported from the sample container to the portion of the apparatus which metered the blood for subsequent dilution and analysis. With relatively larger amounts of blood flowing through the blood analyzer sample metering system, various blood samples could without harm abut at certain points in the blood lines or conduits of the blood analyzer. This abutment of samples resulted in a certain tolerable amount of longitudinal mixing between samples. Because larger amounts of each blood sample flowed through the lines of the blood analyzer metering system, the blood subjected to longitudinal mixing was practically not subjected to analysis by the analyzer in the pragmatic sense when blood was presented to the blood analyzer manually or by the automatic sampling apparatus. Rather, blood subject to such mixing at blood sample interfaces was simply "swept" through the blood analyzer aspiration lines and blood metering valve until nearly unmixed blood reached the latter valve for dilution of the blood and subsequent analysis of blood parameters.
Blood analyzers now have been developed which require very little blood for analysis. However, with smaller sample volumes drawn, cross contamination from one sample to the subsequent sample through longitudinal mixing of the samples in the lines of the blood analyzer sample aspiration probe and blood metering valve becomes a concern, and these newer analyzers therefore use a saline rinse of the aspiration probe and the metering valve and tubing between blood samples. When blood is aspirated through the blood analyzer sampling probe following the saline rinse, there is some longitudinal mixing of saline and the aspirated blood unless means for separation of the saline and blood are employed. To reduce this saline-to-blood-sample carry-over some devices introduce a small segment of air or other gas between the saline and the blood. Heretofore, however, segments of air or other gas have not been used to separate samples in apparatuses which have both an automated and manual aspiration mode. As will be discussed infra, a compatability problem for consistent results between such two modes has existed when gas separation of samples has been attempted in apparatuses which sample both manually and automatically.
Analyzers which use very small amounts of blood (100 microliters) are, for instance, the ELT-800 or ELT-1500 manufactured by Ortho Diagnostic Systems of Westwood, Mass. These analyzers aspirate a small amount of air between the saline rinse liquid and the blood samples to reduce the carry-over from blood to saline during the saline intersample rinse and from saline to blood aspirated into the blood metering valve. The air bubble separates the saline and blood and practically eliminates cross contamination of samples through longitudinal mixing. The air bubble separation is needed simply because larger sample volumes are not available to be "swept" through the lines of the blood metering valve of the blood analyzer to present uncontaminated blood for metering by the analyzer metering valve, for subsequent dilution and analysis.
Analyzers such as the ELT-1500 only permit manual aspiration of blood without automated sampling from closed containers. Automated sampling from closed containers is of importance to reduce the health risk caused by aerosol formation from work with open blood containers as well as a means of cost reduction through automating the process of blood mixing and introduction of aliquots of blood into the blood analyzer. To understand the design requirements for a system for automatic sample introduction from a sampling system such as that described in my '484 patent and into a blood analyzer such as the ELT-1500, it is necessary to understand how blood is manually aspirated and metered in the ELT. An aliquot of sample is aspirated through a sip tube immersed in mixed whole blood contained in an open tube, and the aspirated blood is split into approximately equal portions each of which is drawn through a whole-blood metering tubing having a predetermined length. The blood in each loop is diluted separately. Blood from one loop is diluted and used for white cell enumeration. Blood from the other loop is diluted and used for hemoglobin determination, and after further dilution, for enumeration of red blood cells as well of blood platelets. During manual aspiration of whole-blood into the metering valve, blood is drawn a predetermined length past the metering loops (post-loop distance, PLD). It is critical for accuracy and precision of analytical results that the PLD is consistent for all samples. The PLD depends upon the relationship of the volume of whole-blood aspirated by the analyzer sample aspiration pumps as well as the inside diameter and the length of the sip tube. The critical nature of the post-loop distance is probably due to minute saline-to-blood carry-over as well as a longitudinal concentration gradient of blood components within the whole-blood aspiration tubing near the leading edge end of the blood in said tubing.
To fulfil the above criteria for analytical precision and accuracy, a system for aspiration of whole-blood using an automated mixing and sampling device must therefore expose the automatically introduced blood to conditions practically identical to those occurring when using the manual-sip tube. The tubing used for automated introduction of whole-blood samples (auto-sip tube) must therefore have practically the same diameter and length as the manual-sip tube. To switch from manual to automated whole-blood aspiration into the whole-blood metering valve in the analyzer, a valve must be installed which either connects the manual-sip tube or the auto-sip tube to the metering valve.
To achieve sampling conditions which are consistent between automated and manual modes for consistent analysis, a valving system is needed to isolate the vacuum used for drawing an aliquot of blood from the closed container and for allowing aspiration of part of this sample into the blood analyzer blood metering system under conditions permitting an intact air bubble between saline and samples.
Since blood is drawn from the vacutainer under negative pressure and this negative pressure would disrupt the small air bubble used for carry-over reduction in the auto-sip tube as well as the anaylzer metering valve, means are needed to isolate the vacuum from the analyzer sip tube tip during vacuum assisted aspiration of whole blood from the vacutainer in an automated blood mixing and sampling device such as described in my '484 patent.
To achieve the sample separation for analyzers using small amounts of blood the use of relatively large and/or complicated valves has been attempted. These valves have been disadvantageous because as relatively big valves, more dead volume exists within them which consumes much of an already small sample for operation; as relatively big valves, the more force they consume to open and close; and because they are complicated, they generally are more costly.
It is an object of the present invention to provide a sampling device for fluid materials which will permit the sampling of materials without the longitudinal mixing thereof.
It is another object of the invention to provide valves in a fluid handling and metering system which are easily cleaned, have very small or zero dead volumes, are easily manufactured and require only small forces to open and close.
It is another object of this invention to provide a fluid sampling system which permits automated and manual sample introduction into an analyzer under similar conditions for minimal differences in analytical results generated by the analysis of the samples regardless of whether the sample is introduced manually or automatically.
It is another object of this invention to provide a T-valve for the valving of a fluid flow which is self cleaning, has a very small or zero dead volume, is easily manufactured and requires only a small force to open and close.
It is still another object of this invention to provide a reciprocating, sliding valve for the valving of fluid flow which has a small sliding surface, is self-aligning with a valve seat member, has a straight flow path and is resistant to sticking.